DEPARTMENT OF THE AIR FORCE AIR FORCE CIVIL ENGINEER CENTER INSTALLATION RESTORATION PROGRAM OTIS AIR NATIONAL GUARD BASE, MA 02542-1320

30 October 2020

AFCEC/JBCC 322 East Inner Road Otis ANG Base, MA 02542-1320

Mr. Robert Lim United States Environmental Protection Agency, Region One 5 Post Office Square – Suite 100 Mail Code, OSRR7-3 Boston, MA 02109-3912

Mr. Leonard Pinaud Massachusetts Department of Environmental Protection, Southeast Region 20 Riverside Drive Lakeville, MA 02347

Dear Mr. Lim and Mr. Pinaud:

The Air Force Civil Engineer Center (AFCEC) is hereby submitting the Fact Sheet for No Further Action for 1,4 Dioxane at Chemical Spill-20 dated October 2020.

If you have any questions, please contact me at (508)968-4670 x5613 or email [email protected].

Sincerely,

ROSE FORBES, P.E. Remediation Program Manager

Air Force Civil Engineer Center

Fact Sheet for No Further Action

Fact Sheet October 2020 for 1,4-Dioxane at Chemical Spill-20

The Air Force Civil Summary Engineer Center (AFCEC) is the agency responsible A Supplemental Remedial Investigation (RI) was completed by the Air Force for the for the Installation Restoration Program (IRP) area of contamination identified as the Chemical Spill-20 (CS-20) groundwater plume at the Joint Base Cape Cod at the Joint Base Cape Cod (JBCC) to characterize the nature and extent of 1,4-dioxane (JBCC). The IRP is the program that addresses in groundwater, evaluate its fate and transport, and determine if potentially soil and groundwater unacceptable risks to human health and the environment exist that would warrant contamination resulting from historic uses at JBCC. remedial action.

The U.S. Environmental Based on the conclusions of the Supplemental RI and the risk assessment, 1,4-dioxane Protection Agency (EPA) and the Massachusetts should not be considered a contaminant of concern (COC) at CS-20 and no further Department of action is needed for 1,4-dioxane at CS-20. The U.S. Environmental Protection Agency Environmental Protection (MassDEP) oversee the (EPA) has concurred with this finding, and the Massachusetts Department of AFCEC-led cleanup of the Environmental Protection (MassDEP) will provide their input after consideration of JBCC. comments received during the public comment period for this Fact Sheet. This Fact Sheet is a document that AFCEC is The Air Force is issuing this Fact Sheet as part of its public participation required to issue to fulfill public participation responsibilities under Section 117(a) of the Comprehensive Environmental Response, requirements under Compensation, and Liability Act (CERCLA), and Section 300.430 (f) (2) and (3) of the CERCLA. National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This Fact The purpose of this Fact Sheet is to present the Air Sheet summarizes information that can be found in greater detail in the Supplemental Force’s approach for 1,4- RI and screening-level risk assessment. During the comment period these documents dioxane at the CS-20 groundwater plume and to will be available at the local main libraries in Falmouth, Bourne, Mashpee, and solicit public input to be Sandwich and through AFCEC's online administrative record at: https://ar.afcec- considered by the Air Force and regulatory cloud.af.mil/. The documents are also available for review at the AFCEC agencies prior to finalizing Administrative Record file on JBCC by appointment and at AFCEC's webpage at: this decision. https://www.massnationalguard.org/JBCC/afcec.html. Directions on how to navigate This Fact Sheet has been the online administrative record and webpage can be found at: coordinated with the EPA https://www.massnationalguard.org/JBCC/afcee-documents/how-to-updated.pdf. and the MassDEP.

Words in italics are defined The Air Force encourages the public to view these documents; please contact AFCEC at the end of this document Community Involvement Lead Doug Karson at 508-968-4678, ext. 2 if you have in the glossary section. trouble accessing the documents at the libraries or online.

What do you think?

The Air Force is accepting public comments on this Fact Sheet from 01 August 2020 through 30 August 2020. You do not have to be a technical expert to comment. If you have a comment or concern, AFCEC, EPA, and MassDEP would like to hear from you. Page 8 of this Fact Sheet describes how to submit comments.

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 1 Background

Now known as JBCC (formerly known as the Massachusetts Military Reservation [MMR]) (Figure 1), Otis Air National Guard Base was placed on the National Priorities List in 1989 for investigation under CERCLA. A Federal Facility Agreement, signed in 1991 and subsequently amended, requires AFCEC to take the lead in the Installation Restoration Program activities at JBCC.

The initial recommendation to perform sampling for 1,4-dioxane at the CS-20 groundwater plume was presented in the Final 4th Five-Year Review, 2007-2012 Massachusetts Military Reservation (MMR) Superfund Site Otis Air National Guard Base, MA. A 1,4-dioxane field investigation, completed between October 2013 and June 2014, confirmed the presence of 1,4-dioxane within the CS-20 groundwater plume. The investigation proceeded to a Supplemental RI, which included data collected between August 2015 and May 2016 and data collected between March 2017 and May 2019 during an interim monitoring program. This Fact Sheet presents the Air Force’s decision for 1,4-dioxane at the CS-20 groundwater plume and is based on the conclusions presented in the Supplemental RI report that was finalized in January 2020.

Site Description and History

The CS-20 groundwater site is one of the four Southwest Plumes which also include CS-4, CS-21, and Fuel Spill-29. This area is referred to as the Southwest Operable Unit (SWOU) because it includes part of the southwest portion of JBCC and the area immediately downgradient (southwest) of JBCC within the town of Falmouth, Massachusetts.

The CS-20 groundwater plume was determined to be detached from an unknown source area that was located on JBCC. The CS-20 groundwater plume is defined as the extent of groundwater containing tetrachloroethene (PCE), the CS-20 COC, at concentrations exceeding the Maximum Contaminant Level (MCL) of 5 micrograms per liter (μg/L). The CS-20 PCE groundwater contamination was discovered in March 1997 which led to an RI defining the nature and extent of the CS-20 PCE groundwater plume by 1998. The selected remedy for CS-20 PCE groundwater contamination was presented in a February 2000 Record of Decision (ROD) document called the Final Record of Decision for the CS-4, CS-20, CS-21, and FS-13 Plumes and included the design, construction, and operation of a treatment system to hydraulically capture and treat the PCE groundwater plume, performance and ecological monitoring, and institutional controls. The final design for the CS-20 remedial system consisted of two extraction wells that began operation on 11 January 2006 with a design extraction rate of 775 gallons per minute (gpm), extracted water was treated by granular activated carbon (GAC), and the treated water was returned to the aquifer through reinjection wells and infiltration trenches.

Plume cleanup at CS-20 for PCE progressed faster than predicted. The extraction wells were taken out of operation by 2015 and the remedy at CS-20 transitioned to monitored natural attenuation and institutional controls. The locations of the JBCC and the former 2015 CS-20 plume boundary are shown in Figure 1 on page 3. The changes in the CS-20 plume boundary over time are shown in Figure 2 on page 4. The 2015 CS-20 groundwater plume boundary is used in this Fact Sheet as a location reference; however, by 2016, only one well had PCE concentrations above the MCL of 5 μg/L (69MW1422) and the CS-20 PCE groundwater plume has not been delineated since 2016. The footprint of the 2015 CS-20 groundwater plume occupied approximately 19 acres and was comprised of two individual lobes with approximately 6,700 feet (ft) between the trailing edge and leading edge of the plume, had a maximum width of approximately 500 ft, and was up to 40 ft thick in the aquifer from approximately 145 to 185 ft below ground surface. The maximum historic PCE concentration detected at CS-20 was 98 µg/L in 2005 and the maximum PCE concentration detected at CS-20 in 2015 was 6.7 µg/L at monitoring well 69MW1422. PCE concentrations in only one CS-20 monitoring well (69MW1422) exceeded the MCL in 2018 and PCE was not detected at that location when sampled in 2019. The current data indicate that aquifer restoration is being approached which is approximately five years ahead of the most recent modeling prediction of 2024 for the existing COC (PCE) and approximately 10 years ahead of the aquifer restoration timeframe estimated in the ROD (approximately 2030).

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 2

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Data Source: AFCEC, March 2020 Legend JBCC Boundary From Massachusetts Air National Guard 2011 FIGURE 1 Joint Base Cape Cod JOINT BASE CAPE COD, Former 2015 CS-20 Plume Boundary MASSACHUSETTS (No Longer Delineated) O AFCEC - Joint Base Cape Cod 0 3 6 Miles Y:\Figures\SPEIM\SWOU\2019\SLR\Corel\CS20_19SLR_Fig05.cdr 02/20/2020 jem

Legend Data Source: AFCEC, March 2020 FIGURE 2 Joint Base Cape Cod Boundary Ð! Extraction Well (On) "Ð!! CS-20 VOC Plume Boundary " Extraction Well (Off) CS-20 VOC PLUME BOUNDARY Ð! Reinjection Well (On) Other Plume Boundary "Ð!! " Reinjection Well (Off) TEMPORAL CHANGES Infiltration Gallery AFCEC - Joint Base Cape Cod Treatment System Pipeline 0 1,200 Feet The initial recommendation to perform sampling for 1,4-dioxane at the CS-20 PCE groundwater plume was presented in the Final 4th Five-Year Review. The primary industrial use of 1,4-dioxane was to stabilize solvents, particularly 1,1,1-trichloroethane (TCA), which is less chemically stable than other common solvents such as PCE and trichloroethene. Therefore, 1,4-dioxane is commonly associated with 1,1,1-TCA, or its breakdown product 1,1-dichloroethene (DCE). Both 1,1,1-TCA and 1,1-DCE have been detected in CS-20 monitoring wells in the past.

Summary of the Supplemental Remedial Investigation for 1,4-Dioxane at CS-20

The Supplemental RI field program for 1,4-dioxane was completed between August 2015 and May 2016 and resulted in a 1,4-dioxane dataset from 32 monitoring wells, two extraction wells, two treatment plant ports, one residential well used for drinking water, and one surface water sample collected from Deep Pond (Figure 3 on page 6). One public water supply well located downgradient of the former CS-20 plume was sampled by the Town of Falmouth for 1,4-dioxane in August 2013 and 1,4-dioxane was not detected.

The remediation goal for 1,4-dioxane in groundwater is the risk-based concentration (RBC) of 0.46 µg/L. The EPA’s Superfund process relies on the calculation of a site-specific RBC where Applicable or Relevant and Appropriate Requirement (ARAR)-based standards are not identified. The RBC of 0.46 µg/L replaces the MassDEP Massachusetts Contingency Plan Method-1 Groundwater-1 standard of 0.3 µg/L that was used to assess groundwater data in the June 2016 Draft Supplemental RI Report.

1,4-Dioxane was detected at concentrations exceeding the RBC in two monitoring wells (69MW1422 and 81MW0013B). Since the 1,4-dioxane in groundwater at CS-20 was very limited in extent and concentrations were expected to decrease similar to the observed long-term trend for PCE, a recommendation to implement a 1,4-dioxane interim monitoring program was presented in the June 2016 Draft Supplemental RI Report. Eight CS-20 monitoring wells were sampled for a total of four events between March 2017 and May 2019. 1,4-Dioxane concentrations generally decreased during the interim monitoring period and by October 2018 1,4-dioxane was not detected in seven of the eight wells being monitored. The 1,4-dioxane concentration in the remaining well (69MW1422) fluctuated, decreasing below the RBC in November 2017 (0.2 µg/L) and November 2018 (0.28 µg/L) and then increased to 0.7 µg/L in May 2019. The average 1,4-dioxane concentration in groundwater at this well throughout the interim monitoring period is 0.41 µg/L which is below the RBC of 0.46 µg/L and concentrations in this area are expected to continue to decrease through the processes of natural attenuation similar to the PCE concentration trend observed at this well.

Risk Assessment

The human health risk evaluation for 1,4-dioxane in the Supplemental RI involved comparing groundwater sampling results for 1,4-dioxane to the RBC of 0.46 µg/L for a residential drinking water exposure scenario. A qualitative screening of potential vapor intrusion (VI) risk was completed by comparing 1,4-dioxane groundwater concentrations to the calculated EPA Vapor Intrusion Screening Level of 3,700 µg/L and ecological risks were evaluated by comparing 1,4-dioxane surface water sampling results to the EPA Region 5 ecological screening value of 22,000 µg/L.

The screening-level human health risk assessment concluded there is no unacceptable risk to current or future residents. 1,4-Dioxane is limited in extent and remains in one monitoring well (69MW1422) at concentrations above the RBC of 0.46 µg/L. VI related to 1,4-dioxane at CS-20 is not a concern and there is no unacceptable risk to current and/or future residents from exposure to Deep Pond surface water. In addition, Deep Pond surface water concentrations are well below the ecological screening value for 1,4-dioxane.

The Supplemental RI report was finalized in January 2020 and concluded that no unacceptable risk from 1,4-dioxane exists at the site, 1,4-dioxane is not considered a groundwater COC at CS-20, and no action is needed for 1,4-dioxane in groundwater at CS-20.

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 5 Path: Y:\Figures\General\2020\EmergingContaminants\CS-20_Factsheet\EC_CS20Factsheet_Fig03.mxd Date: 6/8/2020 Time: 5:17:42 PM User: cfitzpat N

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Data Source: AFCEC, March 2020 Legend JBCC Boundary from Massachusetts Air National Guard 2011 Joint Base Cape Cod FIGURE 3 Former 2015 CS-20 Plume Boundary (No Longer Delineated) 1,4-Dioxane Detections in Groundwater: Infiltration Gallery/Trench Monitoring/Extraction/ CS-20 1,4-DIOXANE Residential Well Treatment System Pipeline Public Water Supply Well DETECTIONS IN No Detections )" Bog/Wetland Detection Below or at EPA RBC GROUNDWATER "Ð! Extraction Well (Off) Detection Above EPA RBC AFCEC - Joint Base Cape Cod Public Water Supply Well 1,4-Dioxane EPA RBC = 0.46 µg/L Summary

The initial recommendation to perform sampling for 1,4-dioxane at the CS-20 PCE groundwater plume was presented in the Final 4th Five-Year Review. A presence/absence 1,4-dioxane field investigation was completed between October 2013 and June 2014 and confirmed the presence of 1,4-dioxane in CS-20 groundwater. The Supplemental RI, which included data collected between August 2015 and May 2016 and data collected between March 2017 and May 2019 during an interim monitoring program, was finalized in January 2020. AFCEC’s recommendation for no action for 1,4-dioxane in groundwater at the CS-20 site is based on the following:

• 1,4-Dioxane is only detected in one monitoring well (69MW1422). This monitoring well is screened approximately 80 ft below the water table within a fine to silty sand lithologic unit and concentrations in this area are expected to continue to decrease through the processes of natural attenuation similar to the PCE concentration trend observed at this well. • The screening-level human health risk assessment concluded there is no unacceptable risk to current or future residents from 1,4-dioxane at the CS-20 site under a drinking water exposure scenario. • VI related to 1,4-dioxane at CS-20 is not a concern and there is no unacceptable risk to current and/or future residents from exposure to Deep Pond surface water. In addition, Deep Pond surface water concentrations are well below the ecological screening value for 1,4-dioxane.

Based on the conclusions presented in the Supplemental RI, 1,4-dioxane is not considered a COC at CS-20 and no action is needed for 1,4-dioxane at CS-20.

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 7 How to Submit a Public Comment

Comments can be submitted during the 30-day public comment period which extends from 01 August 2020 to 30 August 2020. All public comments received within the public comment period will be considered by the agencies and documented in a Responsiveness Summary as part of the official record and will be published as an addendum to this Fact Sheet. The Fact Sheet and associated Supplemental RI Report will be posted to AFCEC’s webpage at: https://www.massnationalguard.org/JBCC/afcec.html. They will also be provided to the main libraries in Falmouth, Bourne, Mashpee, and Sandwich. The documents can be viewed by appointment at the IRP Office. The Supplemental RI report is available on AFCEC’s online administrative record at: https://ar.afcec-cloud.af.mil/. Search under Joint Base Cape Cod for document # 599235. A copy of the Fact Sheet can be requested by email by contacting [email protected]. After a final decision is made, the Air Force will announce the issuance of the Final Fact Sheet through a news release to the media and will provide a copy of the Responsiveness Summary to each commenter.

You may submit a formal comment in any of the following ways: 1. Mail written comments to Doug Karson AFCEC/JBCC Attn: CS-20 Plume 322 East Inner Road Otis ANG Base, MA 02542-1320 2. E-mail comments to [email protected] 3. Leave voice mail comments at (508) 968-4678, ext. 2

For Additional Information, Please Contact:

AFCEC/JBCC U.S. EPA MassDEP Doug Karson Darriel Swatts Ellie Donovan Community Involvement Community Involvement Community Involvement Lead Coordinator Coordinator AFCEC/JBCC USEPA Region I MassDEP 322 East Inner Road 5 Post Office Square, Suite 100 20 Riverside Drive Otis ANG Base, MA Boston, MA 02109-3912 Lakeville, MA 02347 02542-5028 Phone: (617) 918-1065 Phone: (508) 946-2866 Phone: (508) 968-4678, ext. 2 [email protected] [email protected] [email protected]

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 8 Glossary

Administrative Record: A collection of documents generated for sites that form the basis for selection of a remedial action and are placed in a central location for public review. Aquifer: An underground geological formation containing usable amounts of groundwater that can supply wells and springs. Applicable or Relevant and Appropriate Requirements (ARAR): Federal and/or state laws and regulations that must be met during the implementation and at the completion of the remedy. Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA): A law that authorizes the federal government to respond directly to releases of hazardous substances that may endanger public health or the environment. It provides authority and funds for the EPA hazardous waste emergency and long-term removal and remedial activities. These activities include establishing the National Priorities List, investigating sites for inclusion on the list, determining their priority level on the list, and conducting and/or supervising the ultimately determined cleanup and other remedial actions. contaminants of concern (COC): Chemicals that are present in soil or groundwater at concentrations above standards and that pose a threat to human health and the environment. downgradient: The area toward which groundwater flows. extraction well: A well that pumps water out of the ground. The contaminated groundwater is then transferred to a treatment facility. Federal Facility Agreement: An agreement between the EPA and individual federal facilities that establishes a procedural and legal framework for investigating and remediating CERCLA sites. Final 4th Five Year Review: Periodic review of site monitoring data to evaluate how the selected remedy(ies) is progressing toward achieving the remedial action objectives. groundwater plume: A body of groundwater containing contaminants exceeding groundwater cleanup standards as defined by multiple samples from multiple wells. Infiltration Trench: A shallow subsurface structure designed to infiltrate treated groundwater. An alternative to reinjection wells. Installation Restoration Program (IRP): The U.S. Department of Defense program implemented at military bases to identify, investigate, and clean up contamination resulting from past operations. At the Joint Base of Cape Cod, AFCEC is the lead agent. institutional controls: Stipulations which reduce or eliminate exposures such as deed restrictions, covenants, or land use restrictions. interim monitoring program: Periodic monitoring, analysis, and reporting of groundwater contaminants to assess changes in the plume extent and concentration over an interim period of time. leading edge: The portion of the plume that is furthest away from the source area and is in the direction where groundwater flows. Maximum Contaminant Level (MCL): the maximum concentration of a given contaminant allowed in drinking water under the federal Safe Drinking Water Act.

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 9 micrograms per liter (µg/L): A measure of concentration of contaminants, which for water is approximately equivalent to parts per billion. National Oil and Hazardous Substances Pollution Contingency Plan (NCP): The federal regulation that sets forth the procedures for implementing cleanup under CERCLA. National Priorities List: The EPA list of uncontrolled or abandoned hazardous waste sites that are priorities for long-term remedial evaluation and response. natural attenuation: The transformation of contaminants into innocuous byproducts (generally carbon dioxide and water) through biodegradation and abiotic transformation as well as the reduction of contaminant concentrations through dispersion, sorption and/or volatilization. Record of Decision (ROD): A document that formally documents the accepted remedy for a given site. The record of decision documents the findings and outcome for each component of the CERCLA process (remedial investigation, feasibility study, proposed plan). reinjection well: A well where treated water is pumped to and can also be used to redirect movement of groundwater. remedial action: Activities conducted to reduce or eliminate the long-term risks to human health or the environment from exposure to contaminants. Remedial Investigation (RI): An investigation to gather and analyze the data necessary to determine the nature and extent of contamination at a site, evaluate the risks to human health and the environment, and provide information for identifying and evaluating options for remedial action. responsiveness summary: A document presenting formal comments received during the public comment period and responses to the comments. risk assessment: An evaluation to determine the risk posed to human health and the environment as a result of exposure to contaminants. risk-based concentration (RBC): Site-specific calculated cleanup standard based on site-specific contaminant information and exposure assumptions. Site Inspection: The initial investigation phase at a site or plume, including data analysis to confirm or deny the presence of contamination (and whether further response actions are needed). trailing edge: The portion of the plume that is closest to the source area from where groundwater flows. vapor intrusion: A process that occurs when there is a migration of vapor-forming chemicals from any subsurface source into an overlying building.

Fact Sheet for No Further Action for 1,4-Dioxane at Chemical Spill-20 – October 2020 – page 10